Hector's dolphin

Hector's dolphin (Cephalorhynchus hectori) is the best-known of the four dolphins in the genusCephalorhynchus and is found only in New Zealand. At about 1.4 m in length, it is one of the smallest cetaceans, and New Zealand's only endemic cetacean.

Maui's dolphin (Cephalorhynchus hectori maui) is a subspecies of Hector's dolphin found off the northwest coast of New Zealand's North Island.[2] It is the most endangered subspecies of marine mammal (other cetaceans with a similarly perilous conservation status inhabit rivers and estuaries only). There are approximately 55 Maui's dolphins remaining.

Māori names for Hector's and Maui's dolphin include Tutumairekurai, Tupoupou and Popoto.

“

... thirty years ago there were over 26,000 Hector's and Maui's dolphins. Today, due to human activity, there is a struggling population of around 7,270 Hector's dolphins — and Maui's are the rarest marine dolphins in the world with around 110 left - WWF Apr. 2007 [3]

Contents

Physical description

Hector's dolphins have a unique rounded dorsal fin.

Hector’s dolphin is the smallest of the delphinids. Mature adults have a total length of 1.2–1.6 m (3 ft 10 in–5 ft 3 in) and weigh 40–60 kg (88–130 lb).[4] The species is sexually dimorphic, with females being slightly longer and heavier than males. The body shape is stocky, with no discernible beak. The most distinctive feature is the rounded dorsal fin, with a convex trailing edge and undercut rear margin.

The overall appearance is pale grey but closer inspection reveals a complex and elegant combination of colours. The back and sides are predominantly light grey, while the dorsal fin, flippers and flukes are black. The eyes are surrounded by a black mask, which extends forward to the tip of the rostrum and back to the base of the flipper. A subtly shaded, crescent shaped black band crosses the head just behind the blowhole. The throat and belly are creamy white, separated by dark grey bands meeting between the flippers. A white stripe extends from the belly onto each flank below the dorsal fin.

At birth, Hector’s dolphin calves have a total length of 60–80 cm (24–31 in) and weigh 8–10 kg (18–22 lb).[5] Their coloration is the same as adults, although the grey has a darker hue. Four to six vertical pale stripes, caused by fetal folds affecting the pigmentation, are present on the calf’s body until an age of about 6 months.

Population and distribution

Hector's dolphins are endemic to the coastal regions of New Zealand. The species has a patchy distribution around the entire South Island, although there are only very occasional sightings in the deep waters of Fiordland. The centres of distribution are on the west coast between Kahurangi Point (41˚S) and Jacksons Bay (44˚S)[6] and on the east coast around Banks Peninsula (43˚S-44˚S).[7] Maui’s dolphin is found only on the west coast of New Zealand’s North Island between 36˚S and 40˚S, with the majority of animals in the central portion of this range between the Manukau and Raglan Harbours.[8]

Abundance has been estimated from a series of five line-transect surveys between 1998 and 2004. The abundance estimate for South Island Hector’s dolphin is 7270 (CV = 16%).[5][6] Current population size is estimated to be 27% of the abundance in 1970 before significant human impacts occurred.[9]

The species has a preference for shallow, coastal waters less than 100 m (330 ft) deep.[10][11] This means they are most commonly seen close to shore, although in shallow regions they have been sighted up to 34 km (21 mi) from the coast. In some areas, there is a pronounced seasonal difference in distribution, with dolphins being sighted further offshore and in deeper water in winter, presumably in response to movements of their prey species.

Ecology and life history

Caught and stranded Hector’s dolphins have provided information on the life history and reproductive parameters of the species. The maximum observed age is 19 years for females and 20 years for males.[4] However, a long term photo-ID project at Banks Peninsula has shown that individuals reach at least 23 years of age. Males attain sexual maturity between five and nine years of age, and females have their first calf between seven and nine years old.[4] The calving interval is two to four years.

These life-history characteristics mean that Hector’s dolphins, like many other small cetaceans, have a low potential for population growth. Maximum population growth rate has been estimated to be 1.8-4.9% per year, although the lower end of this range is probably more realistic.[12]

Hector’s dolphins are believed to be generalist feeders, with prey selection based on size rather than species. Stomach contents of dissected dolphins have included surface schooling fish, mid water fish and squid and a wide variety of benthic species.[3] The largest prey item recovered from a Hector’s dolphin stomach was an undigested red cod weighing 500 g with a standard length of 35 cm.

Natural predators of Hector’s dolphins include sharks and probably orca. Remains of Hector's have been found in sevengill and blue shark stomachs.[14]

Conservation

Hector’s dolphin is covered by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU)[15]

Gillnet threat

Bycatch in bottom-set gillnets has been responsible for the majority of human induced mortality of Hector’s dolphins. Gillnets are made from lightweight mono-filament that is undetectable to the dolphins. Hector's dolphins swim into the nets, get caught and subsequently drown. Some dolphins are able to escape from gillnets, as they are spotted displaying scars consistent with entanglement.[16]

The nationwide estimate for bycatch in commercial gillnets is 110-150 dolphins per year[17] which is far in excess of the level which is considered to be sustainable.[18] Hector’s dolphins face a range of other impacts including trawl bycatch,[19] tourism,[20][21] pollution[3] and habitat modification.

Conservation management for Hector’s dolphin has focussed on reducing gillnet bycatch. The first marine protected area (MPA) for Hector's dolphin was designated in 1988 at Banks Peninsula, where commercial gillnetting was effectively prohibited out to 4 nmi (7.4 km; 4.6 mi) offshore and recreational gillnetting was subject to seasonal restrictions. A second MPA was designated on the west coast of the North Island in 2003. Despite this protection, the Hector’s dolphin population was predicted to continue declining due to bycatch outside the MPAs.[8]

On 15 November 2007, the World Wide Fund for Nature launched an online petition asking Helen Clark, New Zealand's Prime Minister at the time, to introduce emergency measures to protect the Hector's and Maui dolphins.[22] New measures were introduced by the Ministry of Fisheries in 2008 effectively banning gillnetting within 4 n.mi. of the majority of the South Island’s east and south coasts, regulating gillnetting on the South Island’s west coast out to 2 n.mi. (3.7 km) offshore and extending the gillnet ban on the North Island’s west coast to 7 nmi (13 km; 8.1 mi) offshore. There are also restrictions on trawling in some of these areas. For further details on these regulations see the Ministry of Fisheries website.[23] Five marine mammal sanctuaries were designated in 2008 to manage non-fishing related threats to Hector’s and Maui’s dolphin.[24] Their regulations include restrictions on mining and seismic acoustic surveys.

New Zealand free-diver William Trubridge referred to his goal to make the first 100m single breath unassisted dive as "Project Hector" to draw attention to Hector's dolphin. He successfully achieved the dive on December 13, 2010, setting a new world record.[25] A mere three days later Trubridge would surpass his own goal by setting a new world record of 101 meters [26] in a no fins dive on December 16, 2010.

^Baker, A.N., Smith, A.H. and F.B. Pichler. 2002. Geographical variation in Hector's dolphin: recognition of a new subspecies of Cephalorhynchus hectori. Journal of the Royal Society of New Zealand 32: 713-727.